Information storage devices typified by a magnetic disk device are classified into an internal type, in which an information storage device is incorporated in a personal computer (PC) or the like, and an external type, in which an information storage device is disposed outside of a PC or the like. In order to increase storage capacity, there is demand to increase a surface recording density of a magnetic storage medium incorporated in the information storage devices.
In general, reduction of a medium noise is effective in increasing a surface recording density of a magnetic storage medium. Here, a magnetic storage medium of a perpendicular magnetic recording system, which is high in stability of a recording bit in a high recording density, has been put in practical use in recent years. As one of means for reducing the medium noise in the magnetic storage medium of such a perpendicular magnetic recording system, attention has focused on means in which a recording layer magnetically recording information therein is equipped with a so-called granular structure. The granular structure of the recording layer is a structure in which oxide or nitride serving as a non-magnetic material is segregated on a grain interface between magnetic particles. Magnetic separation or isolation of the magnetic particle is excellently achieved in the granular structure. As a consequence, the magnetic particle is pulverized, thereby reducing the medium noise.
In the magnetic storage medium provided with the recording layer of the granular structure, as pulverization or equalization of the magnetic particle or reduction of crystalline orientation dispersion is more promoted, a higher reducing effect of the medium noise can be achieved. In view of this, there have been proposed various methods for further achieving the pulverization or equalization of the magnetic particle and the reduction of the crystalline orientation dispersion (i.e., higher orientation) in the granular structure.
For example, there has been proposed a technique in which an intermediate layer made of a non-magnetic material is disposed right under the recording layer and crystal grains forming the intermediate layer are separated via an interstice, thereby promoting the pulverization of the magnetic particles grown on the crystal grains (see, for example, Japanese Laid-open Patent Publication No. 2005-353256).
Moreover, in order to not only promote the pulverization of the magnetic particle but also achieve the equalization of the magnetic particle or the high orientation, there has been proposed a technique in which a layer called a seed layer is further disposed right under the intermediate layer.
For example, there has been proposed a technique in which a seed layer made of Ni—W in an fcc (face centered cubic) structure is disposed right under an intermediate layer made of Ru in an hcp (hexagonal close packed) structure (see, for example, Japanese Laid-open Patent Publication No. 2007-179598). In addition, there has been proposed a technique in which a seed layer made of Co—Cr—W in an hcp structure is disposed right under an intermediate layer made of Ru in an hcp structure (see, for example, Japanese Laid-open Patent Publication No. 62-102419). Additionally, there has been proposed a technique in which an amorphous seed layer is disposed right under such an intermediate layer (see, for example, Japanese Laid-open Patent Publication No. 2006-309919).
With these techniques, the formation of the intermediate layer on the seed layer can achieve the pulverization, equalization, or high orientation of the crystal grain of Ru in the intermediate layer, and further, can achieve the pulverization, equalization, or high orientation of the magnetic particle in the granular structure of the recording layer formed on the intermediate layer.
Here, a high recording density is being more demanded of the magnetic storage medium in recent years. As for the magnetic storage medium having the seed layer, the medium noise is preferably reduced by further promoting the pulverization of the magnetic particle in the recording layer, thereby achieving a high recording density.